This chapter is from the book

As premade geometry sets that simplify the creation of more complex shapes,
primitives are the building blocks of 3D modeling. To understand this, just take
a look at the objects around you: Everything in nature, no matter how complex,
can be broken down into a few primitive shapessomething you can do right
now with the objects in front of you. Is the object you're looking at built
around many cylinders like a metal chair, or is it a squashed cube like a door
or a wall? Many objects combine a number of different primitives. Take, for
example, the bicycle: Its wheels combine a cylinder (for each spoke) and a slim
torus (which defines the tires' shape). Likewise, you can use a number of
primitives to create a detailed face from a simple sphere, or employ just a few
well-placed cubes to construct a building.

Because they can be manipulated in a variety of ways, primitives have become
an important part of Maya and other 3D programs. NURBS primitives can speed
workflow because the curves have already been drawn and, in many cases, have
been replaced with surface geometry. You can stretch, cut, scale, translate,
trim, and rebuild them, making them essential to your workflow and great
time-savers as well.

Maya includes three primary types of primitives: NURBS, polygons, and
subdivisions. To help you understand which type is appropriate for the task at
hand, this chapter takes a close look at NURBS (Figure 3.1) and polygons (Figure
3.2), explaining the strengths and weaknesses of each. Subdivisions, a more
advanced topic, are covered in detail in Chapter 8.

About NURBS

NURBS curves, surfaces, and primitives are an important part of Maya
modeling. You can use NURBS objects to produce long, smooth surfaces (such as
car hoods) or sharp, angular surfaces (such as stop signs). NURBS objects make
it possible for you to adjust the look of a surface by manipulating just a few
weighted control points (Figure 3.3).

Each of the NURBS curves and surfaces has an associated degree that controls
the smoothness of the NURBS object. A surface degree of 1, or a setting of
linear, will produce a straight connection between each control point, creating
a very angular surface (Figure 3.4). As you raise the degree of the NURBS
object, you create a smoother curve and surface (Figure 3.5). The higher the
degree of the curve, the more points are needed to define it. For more about
NURBS degrees, see Chapter 7.

NURBS, or nonuniform rational B-spline, describes objects whose shapes are
defined by mathematical equations. Luckily for us, Maya takes care of most of
the math behind the scenes. B-spline refers to the underlying curve that defines
all NURBS objects. When creating a NURBS object, you use multiple curves to
produce a wire representation of the surface's appearance. After using
curves to lay down the shape of the surface, you add a skin atop the curves to
create the final surface: This process of creating a surface that extends from
one curve to the next is called lofting (Figure 3.6).

Figure
3.6 The top object has curves only; the bottom object has curves plus a
skin.

You can break down NURBS objects into separate components that work together
to define the shape of the NURBS object. Components include (among others) CVs
(control vertices), edit points, and hullseach of which can be manipulated
to sculpt the surface or define the curves' shapes. (You can manipulate
components together or separately to change the shape of an object.) For more
information on NURBS components, see Chapter 7.